1. Field of the Invention
The present invention relates to a digital image encoding apparatus and method and a corresponding decoding apparatus and method. More particularly, the invention relates to a digital image encoding apparatus and method for recording a signature image using watermarking, and a decoding apparatus and method for restoring the recorded signature image.
Also, the present invention relates to a digital image codec apparatus for recording and restoring a signature image using watermarking.
Further, the present invention relates to a digital image encoding method for recording a signature image using watermarking, and a decoding method for restoring the recorded signature image.
2. Description of the Related Art
Watermarking is a technology in which an original image, i.e., a host image with a signature image secretly embedded thereon, is transmitted. Upon receipt of the original image, only the host image is visible with the signature image being invisible at the receiver. The signature image may be identified by a special detection apparatus, e.g., a decryption apparatus. The watermarking technology is used for providing security and authenticating rights.
FIG. 1 is a conceptual block diagram illustrating a conventional digital image codec apparatus 1 for generating a watermarked image 8 and extracting a signature image 14 from the watermarked image. In the conventional digital image codec apparatus, during encoding, a DCT (Discrete Cosine Transform) 2 is performed on a host image 3 and a secret signature image 4 to be transmitted, thereby extracting DCT coefficients for the respective images. The DCT coefficients are encoded by an encoder 5. Here, the DCT coefficient components of the signature image 4 are encoded by a separate encryption encoder 6 that controls the encryption operation. In such a manner, the DCT coefficients of the host image 3 and the DCT coefficients of the signature image 4 inserted into the DCT coefficients of the host image 3 after being encoded, can be transmitted. An IDCT (Inverse Discrete Cosine Transform) 7 is performed on the DCT coefficients 2A of the host image and the DCT coefficients 2B of the signature image inserted into the DCT coefficients of the host image, thereby obtaining a watermarked image 8 in which only the host image is visible, while the signature image is not visible.
The signature image 4 watermarked on the host image 3 is decoded by a special decryption apparatus to then be restored. During restoration, IDCT is performed on a watermarked image, thereby extracting DCT coefficients thereof. Next, the extracted DCT coefficients 2A obtained by performing DCT on the original host image 3, are separated from the DCT coefficients of the watermarked image at subtractor 10, thereby extracting DCT coefficient components of the encoded signature image. Then, a decoder 11 decodes the DCT coefficient components of the encoded signature image. Here, the encryption decoder 11 performs a control operation for the decryption process. The DCT coefficients of the signature image decoded by the decryption control operation are again IDCT-performed 13, thereby restoring the signature image.
As described above, in the conventional digital image codec apparatus for encoding and decoding a signature image 4 by conventional watermarking, the same original host image 3 as that used at a transmission side must be provided in order to restore the signature image 4 at a receiver side. Also, since the DCT coefficients 2B of the signature image inserted into the DCT coefficients 2A of the host image are transmitted together with the DCT coefficients of the host image, the amount of transmitted data corresponding to the quantity of the signature image is increased.
It is a first object of the present invention to provide a digital image coding apparatus, which can transmit a signature image without increasing the amount of data to be transmitted.
It is a second object of the present invention to provide a digital image decoding apparatus, which can restore a signature image from the data coded by the digital image coding apparatus without the original host image.
It is a third object of the present invention to provide a digital image codec apparatus which can transmit a signature image without increasing the amount of data to be transmitted, and can restore a signature image without the original host image.
It is a fourth object of the present invention to provide a digital image coding method implemented according to the basic operation of the digital image coding apparatus.
It is a fifth object of the present invention to provide a digital image decoding method implemented according to the basic operation of the digital image decoding apparatus.
To achieve the first object of the present invention, there is provided a digital image coding apparatus for recording a signature image on a host image using watermarking, the apparatus including a first discrete wavelet transform portion for receiving a host image and performing discrete wavelet transform thereon, thereby outputting Mxc3x97M discrete wavelet coefficients where M is a predetermined positive integer, a second discrete wavelet transform portion for receiving a signature image and performing discrete wavelet transform thereon, thereby outputting Nxc3x97N discrete wavelet coefficients, where N is a predetermined positive integer smaller than M, a pseudo-random number generator for receiving an encryption code for determining a predetermined rule for generating pseudo-random numbers and generating the pseudo-random numbers in accordance with the predetermined rule corresponding to the encryption code, and a coefficient replacement portion for selecting the replacing locations of Nxc3x97N pixels using the pseudo-random numbers, and replacing the coefficients of the selected Nxc3x97N pixel locations among Mxc3x97M discrete wavelet coefficients with Nxc3x97N wavelet coefficients, thereby outputting replaced Mxc3x97M wavelet coefficients.
To achieve the second object of the present invention, there is provided a digital image coding method for recording a signature image on a host image using watermarking, the method including the steps of receiving a host image and performing discrete wavelet transform thereon, thereby outputting Mxc3x97M discrete wavelet coefficients, where M is a predetermined positive integer, receiving a signature image and performing discrete wavelet transform thereon, thereby outputting Nxc3x97N discrete wavelet coefficients, where N is a predetermined positive integer smaller than M, receiving an encryption code for determining a predetermined rule for generating pseudo-random numbers and generating the pseudo-random numbers in accordance with the predetermined rule corresponding to the encryption code, selecting the replacing locations of Nxc3x97N pixels using the pseudo-random numbers, and replacing the coefficients of the selected Nxc3x97N pixel locations among Mxc3x97M discrete wavelet coefficients with Nxc3x97N wavelet coefficients, thereby outputting replaced Mxc3x97M wavelet coefficients.
To achieve the third object of the present invention, there is provided a digital image decoding apparatus for restoring a signature image embedded on a host image using watermarking, the apparatus including: a pseudo-random number generator for receiving an encryption code and generating pseudo-random numbers in accordance with a predetermined rule according to the encryption code, a coefficient separation portion for setting separating locations of Nxc3x97N pixels using the pseudo-random numbers and separating the wavelet coefficients corresponding to the Nxc3x97N pixel separating locations among Mxc3x97M wavelet coefficients, thereby outputting separated Nxc3x97N wavelet coefficients, and an inverse discrete wavelet transform portion for performing inverse discrete wavelet transform using the separated Nxc3x97N wavelet coefficients, thereby outputting a restored signature image.
To achieve the fourth object of the present invention, there is provided a digital image decoding method for restoring a signature image embedded on a host image using watermarking, the method including the steps of receiving an encryption code and generating pseudo-random numbers in accordance with a predetermined rule according to the encryption code, setting separating locations of Nxc3x97N pixels using the pseudo-random numbers, separating the wavelet coefficients corresponding to the Nxc3x97N pixel separating locations among Mxc3x97M wavelet coefficients, thereby outputting separated Nxc3x97N wavelet coefficients, and performing an inverse discrete wavelet transform using the separated Nxc3x97N wavelet coefficients, thereby outputting a restored signature image.
To achieve the fifth object of the present invention, there is provided a digital image codec apparatus for recording a signature image on a host image using watermarking, and restoring the signature image from a watermarked image having the signature image embedded thereon, the apparatus including a first discrete wavelet transform portion for receiving a host image and performing discrete wavelet transform thereon, thereby outputting Mxc3x97M discrete wavelet coefficients where M is a predetermined positive integer, a second discrete wavelet transform portion for receiving a signature image and performing discrete wavelet transform thereon, thereby outputting Nxc3x97N discrete wavelet coefficients, where N is a predetermined positive integer smaller than M, a first pseudo-random number generator for receiving an encryption code for determining a predetermined rule for generating pseudo-random numbers and generating the pseudo-random numbers in accordance with the predetermined rule corresponding to the encryption code, a coefficient replacement portion for selecting the replacing locations of Nxc3x97N pixels using the pseudo-random numbers, and replacing the coefficients of the selected Nxc3x97N pixel locations among Mxc3x97M discrete wavelet coefficients with Nxc3x97N wavelet coefficients, thereby outputting replaced Mxc3x97M wavelet coefficients, a second pseudo-random number generator for receiving the encryption code and generating pseudo-random numbers in accordance with a predetermined rule corresponding to the encryption code, a coefficient separation portion for setting separating locations of Nxc3x97N pixels using the pseudo-random numbers, and separating the wavelet coefficients corresponding to the Nxc3x97N pixel separating locations among Mxc3x97M wavelet coefficients for the combined host image, thereby outputting Nxc3x97N wavelet coefficients of the signature image, and an inverse discrete wavelet transform portion for performing inverse discrete wavelet transform using the separated Nxc3x97N wavelet coefficients, thereby outputting a restored signature image.
Finally, the invention comprises a program media having stored thereon a computer program embodying the foregoing methods.